One of the most amazing elements that can form a huge variety of compounds of organic and inorganic nature is carbon. This element is so unusual in its properties that even Mendeleev predicted a great future for it, talking about features that have not yet been disclosed.
Later it was practically confirmed. It became known that it is the main biogenic element of our planet, which is part of absolutely all living beings. In addition, capable of existing in forms that are radically different in all respects, but at the same time consist only of carbon atoms.
In general, this structure has many features, and we will try to deal with them in the course of the article.
Carbon: formula and position in the system of elements
In the periodic system, the element carbon is located in the IV (according to the new model in 14) group, the main subgroup. Its serial number is 6, and its atomic weight is 12.011. The designation of an element with the sign C indicates its name in Latin - carboneum. There are several different forms in which carbon exists. Its formula is therefore different and depends on the specific modification.
However, for writing reaction equations, the notation is specific,of course have. In general, when talking about a substance in its pure form, the molecular formula of carbon C is adopted, without indexing.
Element discovery history
This element itself has been known since antiquity. After all, one of the most important minerals in nature is coal. Therefore, for the ancient Greeks, Romans and other nationalities, he was not a secret.
Besides this variety, diamonds and graphite were also used. There were many confusing situations with the latter for a long time, since often, without analysis of the composition, such compounds were taken for graphite, such as:
- silver lead;
- iron carbide;
- molybdenum sulfide.
They were all painted black and therefore considered graphite. Later, this misunderstanding was cleared up, and this form of carbon became itself.
Since 1725, diamonds have been of great commercial importance, and in 1970, the technology of obtaining them artificially has been mastered. Since 1779, thanks to the work of Karl Scheele, the chemical properties that carbon exhibits have been studied. This was the beginning of a series of important discoveries in the field of this element and became the basis for finding out all its most unique features.
Carbon isotopes and distribution in nature
Despite the fact that the element in question is one of the most important biogenic, its total content in the mass of the earth's crust is 0.15%. This is due to the fact that it is subjected to constant circulation, a natural cycle in nature.
In general, there are severalmineral compounds containing carbon. These are such natural breeds as:
- dolomites and limestones;
- anthracite;
- oil shale;
- natural gas;
- coal;
- oil;
- lignite;
- peat;
- bitumen.
Besides this, we should not forget about living beings, which are just a repository of carbon compounds. After all, they formed proteins, fats, carbohydrates, nucleic acids, which means the most vital structural molecules. In general, in the conversion of dry body weight out of 70 kg, 15 falls on a pure element. And so it is with every person, not to mention animals, plants and other creatures.
If we consider the composition of air and water, that is, the hydrosphere as a whole and the atmosphere, then there is a mixture of carbon-oxygen, expressed by the formula CO2. Dioxide or carbon dioxide is one of the main gases that make up the air. It is in this form that the mass fraction of carbon is 0.046%. Even more carbon dioxide is dissolved in the waters of the oceans.
The atomic mass of carbon as an element is 12.011. It is known that this value is calculated as the arithmetic average between the atomic weights of all isotopic species that exist in nature, taking into account their prevalence (as a percentage). This is also the case for the substance in question. There are three main isotopes in which carbon is found. This is:
- 12С - its mass fraction in the vast majority is 98.93%;
- 13C -1.07%;
- 14C - radioactive, half-life 5700 years, stable beta emitter.
In the practice of determining the geochronological age of samples, the radioactive isotope 14С is widely used, which is an indicator due to its long decay period.
Allotropic modifications of an element
Carbon is an element that exists as a simple substance in several forms. That is, it is capable of forming the largest number of allotropic modifications known today.
1. Crystalline variations - exist in the form of strong structures with regular atomic-type lattices. This group includes varieties such as:
- diamonds;
- fullerenes;
- graphites;
- carbines;
- lonsdaleites;
- carbon fibers and tubes.
All of them differ in the structure of the crystal lattice, in the nodes of which there is a carbon atom. Hence the completely unique, dissimilar properties, both physical and chemical.
2. Amorphous forms - they are formed by a carbon atom, which is part of some natural compounds. That is, these are not pure varieties, but with impurities of other elements in small quantities. This group includes:
- activated carbon;
- stone and wood;
- soot;
- carbon nanofoam;
- anthracite;
- glassy carbon;
- a technical kind of substance.
They are also united by featuresstructures of the crystal lattice, explaining and manifesting properties.
3. Compounds of carbon in the form of clusters. Such a structure in which atoms are closed in a special conformation hollow from the inside, filled with water or the nuclei of other elements. Examples:
- carbon nanocones;
- astralens;
- dicarbon.
Physical properties of amorphous carbon
Due to the wide variety of allotropic modifications, it is difficult to identify any common physical properties for carbon. It's easier to talk about a specific form. For example, amorphous carbon has the following characteristics.
- At the heart of all forms are fine-crystalline varieties of graphite.
- High heat capacity.
- Good conductive properties.
- Carbon density is about 2 g/cm3.
- When heated above 1600 0C, a transition to graphite forms occurs.
Soot, charcoal and stone varieties are widely used for industrial purposes. They are not a manifestation of carbon modification in its pure form, but contain it in very large quantities.
Crystalline carbon
There are several options in which carbon is a substance that forms regular crystals of various types, where atoms are connected in series. As a result, the following modifications are formed.
- Diamond. The structure is cubic, in which four tetrahedra are connected. As a result, all covalent chemical bonds of each atommaximally saturated and durable. This explains the physical properties: the density of carbon is 3300 kg/m3. High hardness, low heat capacity, lack of electrical conductivity - all this is the result of the structure of the crystal lattice. There are technically obtained diamonds. They are formed during the transition of graphite to the next modification under the influence of high temperature and a certain pressure. In general, the melting point of diamond is as high as the strength - about 3500 0C.
- Graphite. The atoms are arranged similarly to the structure of the previous substance, however, only three bonds are saturated, and the fourth one becomes longer and less strong, it connects the "layers" of the hexagonal rings of the lattice. As a result, it turns out that graphite is a soft, greasy black substance to the touch. It has good electrical conductivity and has a high melting point - 3525 0C. Capable of sublimation - sublimation from a solid state to a gaseous state, bypassing the liquid state (at a temperature of 3700 0С). The density of carbon is 2.26 g/cm3, which is much lower than that of diamond. This explains their different properties. Due to the layered structure of the crystal lattice, it is possible to use graphite for the manufacture of pencil leads. When swiped across the paper, the flakes peel off and leave a black mark on the paper.
- Fullerenes. They were opened only in the 80s of the last century. They are modifications in which carbons are interconnected in a special convex closed structure, which has in the centeremptiness. And the form of a crystal - a polyhedron, the correct organization. The number of atoms is even. The most famous form of fullerene is С60. Samples of a similar substance were found during research:
- meteorites;
- bottom sediments;
- folgurite;
- shungite;
- outer space, where they were contained in the form of gases.
All varieties of crystalline carbon are of great practical importance, since they have a number of properties useful in engineering.
Reactivity
Molecular carbon exhibits low reactivity due to its stable configuration. It can be forced to enter into reactions only by imparting additional energy to the atom and forcing the electrons of the outer level to evaporate. At this point, the valency becomes 4. Therefore, in compounds, it has an oxidation state of + 2, + 4, - 4.
Practically all reactions with simple substances, both metals and non-metals, proceed under the influence of high temperatures. The element in question can be both an oxidizing agent and a reducing agent. However, the latter properties are especially pronounced in it, and this is the basis for its use in the metallurgical and other industries.
In general, the ability to enter into chemical interaction depends on three factors:
- dispersion of carbon;
- allotropic modification;
- reaction temperature.
Thus, in some cases there is an interaction with the followingsubstances:
- non-metals (hydrogen, oxygen);
- metals (aluminum, iron, calcium and others);
- metal oxides and their s alts.
Does not react with acids and alkalis, very rarely with halogens. The most important of the properties of carbon is the ability to form long chains with each other. They can close in a cycle, form branches. This is how the formation of organic compounds, which today number in the millions. The basis of these compounds are two elements - carbon, hydrogen. Other atoms may also be included: oxygen, nitrogen, sulfur, halogens, phosphorus, metals and others.
Main compounds and their characteristics
There are many different compounds that contain carbon. The formula of the most famous of them is CO2 - carbon dioxide. However, in addition to this oxide, there is also CO - monoxide or carbon monoxide, as well as suboxide C3O2.
Among the s alts that contain this element, the most common are calcium and magnesium carbonates. So, calcium carbonate has several synonyms in the name, since it occurs in nature in the form:
- chalk;
- marble;
- limestone;
- dolomite.
The importance of alkaline earth metal carbonates is manifested in the fact that they are active participants in the formation of stalactites and stalagmites, as well as groundwater.
Carbonic acid is another compound that forms carbon. Its formula isH2CO3. However, in its usual form, it is extremely unstable and immediately decomposes into carbon dioxide and water in solution. Therefore, only its s alts are known, and not itself, as a solution.
Carbon halides - are obtained mainly indirectly, since direct synthesis takes place only at very high temperatures and with a low yield of the product. One of the most common - CCL4 - carbon tetrachloride. A toxic compound that can cause poisoning if inhaled. Obtained by reactions of radical photochemical substitution of hydrogen atoms in methane.
Metal carbides are carbon compounds in which it exhibits an oxidation state of 4. It is also possible to have associations with boron and silicon. The main property of carbides of some metals (aluminum, tungsten, titanium, niobium, tantalum, hafnium) is high strength and excellent electrical conductivity. Boron carbide В4С is one of the hardest substances after diamond (9.5 according to Mohs). These compounds are used in engineering, as well as in the chemical industry, as sources for the production of hydrocarbons (calcium carbide with water leads to the formation of acetylene and calcium hydroxide).
Many metal alloys are made using carbon, thereby significantly increasing their quality and technical characteristics (steel is an alloy of iron and carbon).
Special attention deserves numerous organic compounds of carbon, in which it is a fundamental element capable of combining with the same atoms into long chains of various structures. These include:
- alkanes;
- alkenes;
- arenas;
- proteins;
- carbs;
- nucleic acids;
- alcohols;
- carboxylic acids and many other classes of substances.
Use of carbon
The importance of carbon compounds and its allotropic modifications in human life is very high. You can name a few of the most global industries to make it clear that this is true.
- This element forms all types of fossil fuels from which a person receives energy.
- The metallurgical industry uses carbon as the strongest reducing agent to obtain metals from their compounds. Carbonates are also widely used here.
- Construction and the chemical industry consume a huge amount of carbon compounds to synthesize new substances and obtain the necessary products.
You can also name such sectors of the economy as:
- nuclear industry;
- jewellery;
- technical equipment (lubricants, heat-resistant crucibles, pencils, etc.);
- determination of the geological age of rocks - radioactive tracer 14С;
- carbon is an excellent adsorbent, which makes it suitable for making filters.
Circulation in nature
The mass of carbon found in nature is included in a constant cycle that cycles every second around the globe. Thus, the atmospheric source of carbon - CO2, is absorbedplants and is released by all living beings in the process of respiration. Once in the atmosphere, it is absorbed again, and so the cycle does not stop. At the same time, the death of organic residues leads to the release of carbon and its accumulation in the earth, from where it is then again absorbed by living organisms and released into the atmosphere in the form of gas.
